On how the mechanochemical and co-precipitation synthesis method changes the sensitivity and operating range of the Ba2Mg1-xEuxWO6 optical thermometer

Comparative properties of ZnO modified Au/Fe nanocomposite: electronic, dynamic, and locator annealing investigation

CONTEXT

A computational representation was used to model the doping and nanomodification of ZnO nanoparticles incorporated in Au/Fe nanocomposite. Au/Fe nanostructure was geometrically and discussed to investigate its electronic properties such electronic band structure and PDOS spectra. Moreover, the ZnO interacted with Au/Fe system was illustrated concerning the modified properties present on the surface of the nanocomposite as it may behave different attribution of band gap evaluated after ZnO modification included. Molecular dynamic simulation of the whole nano system was studied to predict the system stability concerning temperature and energy parameters during 100 ps simulation time. The most effective models under investigation were evaluated using adsorption annealing computations associated with the adsorption energy surface. A highly stable energetic adsorption system was anticipated by the periodic adsorption-annealing calculation.

METHODS

Au and Fe pure metals nanostructures were studied as a separate molecule with (0 0 1) plane surface for optimum energy minimization. Dmol3 module in/materials studio software was utilized for this protocol. The designed Au/Fe layers for nanostructure building material was computationally optimized, where DFT level was considered involving generalized gradient approximation (GGA) with Perdew-Burke-Ernzerh (PBE) exchange functional. In the computations of the structure matrix simulation, the global orbital cutoff was selected. To address the weak quantification of the standard DFT functionals, Tkatchenko-Schefer (TS) (DFT + D) was utilized to precisely correct the pairwise dispersion of the functionals. The electrical parameters were interpreted using the reciprocal space of the ultrasoft pseudopotential representation. To overcome the issues of self-electron interaction, the nonlocal hybrid functional with PBE0 method was utilized to calculate the electronic properties of the studied systems. The computations generated are predicated on a particular trajectory of the gamma k-point band energy interpolations proposed in this examination. An investigation into the position of adsorption came after geometric optimization. Adsorbed on an optimized Au/Fe surface, ZnO nanostructure was computationally explored using the Dmol3 simulation software.

Effect of A-Cation Radius on the Structure, Luminescence, and Temperature Sensing of Double Perovskites A2MgWO6 Doped with Dy3+ (A = Ca, Sr, Ba)

Herein, we report a case of A2MgWO6 (A = Ca, Sr, Ba) doped with 2%Dy3+, 2%Li+, in which the influences of the cation substitution are exhibited through the crystal structure, the charge transfer band (O2--W6+), the emission spectrum, the color of the luminescence, and the luminescent decay time. The substitution of Ca2+ and Sr2+ ions for larger ions (Ba2+) led to the crystal structure alteration from cubic to monoclinic and tetragonal, respectively. These structure changes also lowered the crystallography symmetry site of Dy3+, tuned the color of the emitted light from the whitish to yellowish region, and caused a blue shift of the CTB. Furthermore, a significant decline in the lifetime of the 4F9/2 → 6H13/2,15/2 transitions was noticed, from 748, 199, to 146 μs corresponding to Ba, Sr, Ca sample owing to the reduction in the local symmetry of Dy3+. Moreover, the thermal sensing properties of 2%Dy3+-doped samples were investigated based on the fluorescence intensity ratio technique in the range of 80-325 K. Under 266 nm excitation wavelength, the maximum relative sensitivity of the investigated samples was remarkably enhanced from 2.26%/K, 3.04%/K, to 4.38%/K corresponding to Ba, Ca, and Sr samples, respectively. In addition to providing a comprehensive understanding of the effects of compositional modifications on the optical properties, the results also present a viable pathway to manipulate the temperature sensing performance.

Effect of Sr2+ ions on the structure, up-conversion emission and thermal sensing of Er3+, Yb3+ co-doped double perovskite Ba(2-x)SrxMgWO6 phosphors

Investigating the effect of different phases on the optical performance is crucial for thermal sensing phosphor materials. Ba_(2-x)Sr_xMgWO₆:Er³⁺, Yb³⁺, K⁺ double perovskite phosphors were successfully prepared using a high-temperature solid-phase method. The dominant up-conversion luminescent (UCL) mechanism was deduced by analyzing the power-dependence spectra and energy level diagrams. By X-ray diffraction tests and tolerance factor calculations, it was demonstrated that the substitution of Sr²⁺ ions for Ba²⁺ ions led to the phase changing from cubic to tetragonal. The phase transition led to a decrease in the crystallographic symmetry of the compounds and changes in the optical thermometric properties. The optical temperature sensing properties were investigated using the fluorescence intensity ratio of thermally coupled energy levels (²H_11/2 and ⁴S_3/2 to the ground state energy level ⁴I_15/2) of Er³⁺ ions in Ba₂MgWO₆, BaSrMgWO₆ and Sr₂MgWO₆. The maximum absolute sensitivities obtained for Ba₂MgWO₆, BaSrMgWO₆ and Sr₂MgWO₆ doped with 7% Er³⁺, 2% Yb³⁺ and 9% K⁺ were 6.77 × 10^-4 K^-1, 10.09 × 10^-4 K^-1 and 23.4 × 10^-4 K^-1, respectively. The comparison revealed that the phase transition caused an increase in the luminescence intensity and absolute sensitivity. This provides a useful pathway for modulating the subsequent thermometric performance.

Studies of the Structure and Optical Properties of BaSrMgWO6 Thin Films Deposited by a Spin-Coating Method

Highly transparent thin films with the chemical formula BaSrMgWO₆ were deposited by spin coating using a solution of nitrates of Ba, Sr, and Mg and ammonium paratungstate in dimethylformamide with a Ba:Sr:Mg:W ratio = 1:1:1:1. XRD, SEM, EDX, and XPS investigations evidenced that annealing at 800 °C for 1 h results in an amorphous structure having a precipitate on its surface, and that supplementary annealing at 850 °C for 45 min forms a nanocrystalline structure and dissolves a portion of the precipitates. A textured double perovskite cubic structure (61.9%) was found, decorated with tetragonal and cubic impurity phases (12.7%), such as BaO₂, SrO₂, and MgO, and an under-stoichiometric phase (24.4%) with the chemical formula Ba_2-(x+y) Sr_xMg_yWO₅. From transmittance measurements, the values of the optical band gap were estimated for the amorphous (E_gdir = 5.21 eV, E_gind = 3.85 eV) and nanocrystalline (E_gdir = 4.69 eV, E_gind = 3.77 eV) phases. The presence of a lattice disorder was indicated by the high Urbach energy values and weak absorption tail energies. A decrease in their values was observed and attributed to the crystallization process, lattice strain diminution, and cation redistribution.